1. Field of the Invention
The present invention relates to a liquid crystal display device. More particularly, the present invention relates to a semi-transparent liquid crystal display device including a retardation film on the side of a color filter substrate.
2. Description of the Related Art
A semi-transparent liquid crystal display device including a transparent element and a reflective element in a single sub-pixel is used as a display for portable device.
FIG. 18 and FIG. 19 are principal part sectional views showing an outline configuration of a single sub-pixel of a conventional IPS-based semi-transparent liquid crystal display device.
In FIG. 18 and FIG. 19, SUB1 denotes a glass substrate (also referred to as TFT substrate) on which a thin-film transistor constituting an active element, a pixel electrode, an opposing electrode (not shown), etc. are formed; SUB2, a glass substrate (also referred to as color filter substrate) on which a color filter, a black matrix, etc. are formed; MR, a gap adjustment layer; RAL, a diffuse reflection layer having an irregular surface; SPA, a columnar spacer; POL1 and POL2, polarizing plates; and RET1 and RET2, retardation plates.
Reference numeral 30 denotes a transparent element, and 31, a reflective element. The cell gap length of the reflective element 31 is set to about a half of that of the transparent element 30 by means of a gap adjustment layer (MR) in order to set almost the same optical path length both for the transparent element 30 and the reflective element 31 because light passes twice (in forward and return paths) through the reflective element 31.
With the semi-transparent liquid crystal display device shown in FIG. 18, an adjustment layer (MR) is formed on the side of the glass substrate (SUB2). With the semi-transparent liquid crystal display device shown in FIG. 19, a gap adjustment layer (MR) is formed on the side of the glass substrate (SUB1). With the semi-transparent liquid crystal display devices shown in FIG. 18 and FIG. 19, the main surface side of the glass substrate (SUB2) is the observation side.
With the conventional IPS-based semi-transparent liquid crystal display device, polarizing plates (POL1, POL2) with built-in retardation plates (RET1, RET2) are used as shown in FIG. 18 and FIG. 19, and therefore the retardation plates (RET1, RET2) also affect the light which penetrates through the transparent element 30, adversely affecting the optical characteristics and causing a problem that it is difficult to make the optical characteristics of the transparent element 30 and the reflective element 31 compatible with each other.
The following device is known to solve the above-mentioned problem: an IPS-based semi-transparent liquid crystal display device which includes a built-in retardation plate only in the reflective element 31 on the side of the glass substrate (SUB2) (refer to JP-A-2005-338256).
JP-A-2005-338256 discloses a technique related to the invention of the present application.